XIV FUNDAMENTAL TROBLEMS 437 



by the action of the fundamental laws of growth. Admitting 

 that such laws have determined some of the main divisions of 

 the animal and vegetable kingdom, have originated certain 

 important organs, and have been the fundamental cause of 

 certain lines of development, yet at every step of the process 

 these laws must have acted in entire subordination to the law of 

 natural selection. No modification thus initiated could have 

 advanced a single step, unless it were, on the whole, a useful 

 modification ; while its entire future course would be necessarily 

 subject to the laws of variation and selection, by which it 

 would be sometimes checked, sometimes hastened on, sometimes 

 diverted to one purpose, sometimes to another, according as the 

 needs of the organism, under the special conditions of its 

 existence, recjuired such modification. We need not deny that 

 such laws and influences may have acted in the manner 

 suggested, but what we do deny is that they could possibly 

 escape from the ever-present and all-powerful modifying eftects 

 of variation and natural selection.^ 



TFeisviann's Theory of Heredity. 



Professor August "Weismann has put forth a new theory of 

 heredity founded upon the "continuity of the germ-plasm," 

 one of the logical consecjuences of which is, that acquired 

 characters of whatever kind are not transmitted from parent to 

 offspring. As this is a matter of vital importance to the theory 

 of natural selection, and as, if well founded, it strikes away the 

 foundations of most of the theories discussed in the present 

 chapter, a brief outline of Wcismann's views must be attempted, 



^ 111 an essay on "The Duration of Life," forming part of the transhation 

 of Dr. Weismanu's papers already referred to, the author still further 

 extends the sphere of natural selection by showing that the average duration 

 of life in each sjjecies has been determined by it. A certain length of life is 

 essential in order that the species may produce offspring sufficient to ensure 

 its continuance under the most unfavourable conditions ; and it is shown that 

 the remarkable inequalities of longevity in different species and gi-oups may 

 be thus accounted for. Yet more, the occurrence of death in the higher 

 organisms, in place of the continued survival of the unicellular organisms how- 

 ever much they may increase by subdivision, may be traced to the same great 

 law of utility for the race and survival of the fittest. The whole essay is of 

 exceeding interest, and will repay a careful perusal. A similar idea occurred 

 to the present writer aliout twenty years back, and was briefly noted down at 

 the time, but subsequently forgotten. 



